Investigators are searching the wreckage for the trains' devices that record operating speeds and commands, NTSB member Debbie Hersman said.

Each train had six cars and was capable of holding as many as 1,200 people. Hersman said the trains were bound for downtown. That would mean they were less likely to be filled during the evening rush hour.

The trains had pulled out of the Takoma Park station and were headed in the direction of the Fort Totten station.

More than 200 firefighters from Washington, Maryland and Virginia eventually converged on the scene.

Sabrina Webber, 45, a real estate agent who lives in the neighborhood, said the first rescuers to arrive had to use the Jaws of Life to pry open a wire fence along the rail line to get to the train. Webber raced to the scene after hearing a boom like a “thunder crash” and then sirens. She said there was no panic among the survivors.

Passenger Jodie Wickett, a nurse, told CNN she was seated on one train, sending text messages on her phone, when she felt the impact. Wickett said she sent a message to someone that it felt like the train had hit a bump.

“From that point on, it happened so fast, I flew out of the seat and hit my head.,” she said.

Wickett said she stayed at the scene and tried to help. She said “people are just in very bad shape.”

“The people that were hurt, the ones that could speak, were calling back as we called out to them,” she said. “Lots of people were upset and crying, but there were no screams.”

One man said he was riding a bicycle across a bridge over the Metro tracks when the sound of the crash got his attention.

At Howard University Hospital, emergency room physician Johnnie Ford said a 14-year-old girl suffered two broken legs in the accident. A 20-year-old male patient “looked like he had been tumbled around quite a bit, bumps and bruises from head to toe,” Ford said.

Homeland Security Department spokeswoman Amy Kudwa said less than two hours after the crash that federal authorities had no indication of any terrorism connection.

Yesterday's crash was the third major subway or commuter rail crash in a big city in the past nine months. In the earlier accidents:

•In September 2008, a commuter rail train and a freight train crashed in Los Angeles, killing 25 people. The crash was blamed on an engineer on the commuter rail sending text messages on a cell phone.

•Last month, about 50 people were injured in Boston when one trolley rear-ended another. The conductor admitted to sending a text message when the crash occurred.

No reason was given for the Washington crash, but some safety experts are concerned about the recent increase.

“I'm not sure if everyone in the safety system is paying the proper attention that needs to be paid,” said Barry Sweedler, a San Francisco-based safety consultant and former investigator and manager at the NTSB. “These things shouldn't be happening.”